I believe this is the correct answer. The people in the "crowd" holding the torches were also dancing in synchronization with parts of the music, so they obviou

I believe this is the correct answer. The people in the "crowd" holding the torches were also dancing in synchronization with parts of the music, so they obviously practiced beforehand and I'm tempted to assume they each had an assigned spot to stand in at certain times. Given that they were in predetermined positions, the LED synchronization would be trivial.